One of Elizabeth Barrett Browning's most famous poems, Sonnet 43, describes her love for her husband-to-be, Robert Browning. I think you are referring to how she loves him with her entire being rather than the poem saying she loves his entire being. No doubt she loves everything about him, but that isn't the focus of the poem.
It's difficult for her to measure her love since it is infinite. This love contains every emotion you can imagine and grows with each day. It even extends beyond death. She uses metaphors (direct comparisons) to compare the depth of her love, such as to a soldier fighting for freedom. She believes the heart and soul has no restraints, so her love for Robert has no restraints. There are no limits to what the human soul and heart can feel. She lets us picture how vast her love is through images by using words such as "depth" and "breadth". She also believes we must never take love for granted or become too comfortable in our love for someone else. Loving another person is an on-going process. She loves him freely and purely.